Wicked Prince by Mary E. Twomey

Keeping war from breaking out isn’t the best reason to marry someone, but Lily knows it’s the only way to keep the world from going up in flames.
Though Lily’s marriage to Prince Destino was fake, it’s never felt more real than when she accepts a second proposal from Prince Alexavier, her childhood friend. While Drexdenberg is gearing up to defend themselves against the other two territories, the three princes escape with their princess to fae territory in hopes that they can talk some sense into the broken and out-of-touch monarchy.
Lily thought she could outrun the sins of her past, but moving back into the country that spat her out when she was just a girl threatens to bring her dark deeds to light. The possibility of her husbands turning against her when they discover her sins is one thing, but when she has to go head-to-head with the fae king and General Klein, Lily knows there will be no turning back. With General Klein intent on taking Lily out of the picture, the three princes and their bride will have to decide if the fae are worth saving.
When King Ronin comes to her with an offer she can’t refuse, Lily worries the only solution to the world’s wars won’t just tear out her heart, but also might require her very last breath.